void FormatArg::initSlow()

in folly/Format.cpp [232:360]
109 lines of code
37 McCabe index (conditional complexity)

void FormatArg::initSlow() {
  auto b = fullArgString.begin();
  auto end = fullArgString.end();

  // Parse key
  auto p = static_cast<const char*>(memchr(b, ':', size_t(end - b)));
  if (!p) {
    key_ = StringPiece(b, end);
    return;
  }
  key_ = StringPiece(b, p);

  if (*p == ':') {
    // parse format spec
    if (++p == end) {
      return;
    }

    // fill/align, or just align
    Align a;
    if (p + 1 != end &&
        (a = formatAlignTable[static_cast<unsigned char>(p[1])]) !=
            Align::INVALID) {
      fill = *p;
      align = a;
      p += 2;
      if (p == end) {
        return;
      }
    } else if (
        (a = formatAlignTable[static_cast<unsigned char>(*p)]) !=
        Align::INVALID) {
      align = a;
      if (++p == end) {
        return;
      }
    }

    Sign s;
    auto uSign = static_cast<unsigned char>(*p);
    if ((s = formatSignTable[uSign]) != Sign::INVALID) {
      sign = s;
      if (++p == end) {
        return;
      }
    }

    if (*p == '#') {
      basePrefix = true;
      if (++p == end) {
        return;
      }
    }

    if (*p == '0') {
      enforce(align == Align::DEFAULT, "alignment specified twice");
      fill = '0';
      align = Align::PAD_AFTER_SIGN;
      if (++p == end) {
        return;
      }
    }

    auto readInt = [&] {
      auto const c = p;
      do {
        ++p;
      } while (p != end && *p >= '0' && *p <= '9');
      return to<int>(StringPiece(c, p));
    };

    if (*p == '*') {
      width = kDynamicWidth;
      ++p;

      if (p == end) {
        return;
      }

      if (*p >= '0' && *p <= '9') {
        widthIndex = readInt();
      }

      if (p == end) {
        return;
      }
    } else if (*p >= '0' && *p <= '9') {
      width = readInt();

      if (p == end) {
        return;
      }
    }

    if (*p == ',') {
      thousandsSeparator = true;
      if (++p == end) {
        return;
      }
    }

    if (*p == '.') {
      auto d = ++p;
      while (p != end && *p >= '0' && *p <= '9') {
        ++p;
      }
      if (p != d) {
        precision = to<int>(StringPiece(d, p));
        if (p != end && *p == '.') {
          trailingDot = true;
          ++p;
        }
      } else {
        trailingDot = true;
      }

      if (p == end) {
        return;
      }
    }

    presentation = *p;
    if (++p == end) {
      return;
    }
  }

  error("extra characters in format string");
}